mysql 常用语句笔记

1. 根据多个字段查询（按照status升序和last_login_time降序进行排序，如果status为3的话，置为0即可以显示在最前面）

ORDER BY (CASE WHEN status=3 THEN 0 ELSE 1 END), status ASC, last_login_time DESC

2.多个表联合查询 如何连接

SELECT a.id,a.name,a.status, c.flag FROM table1 AS a LEFT JOIN table2 AS b ON a.id=b.app_id LEFT JOIN table3 AS c ON b.name=c.name WHERE a.flag='6' AND c.state='error'  group by a.id